Regulatory Matters - Schedule of Utilities Rate Plans (O&R New York-Electric) (Details) - USD ($) $ in Millions	12 Months Ended				36 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2027	Dec. 31, 2024
Public Utilities, General Disclosures [Line Items]
Accrued unbilled revenue	$ 821.0	$ 848.0				$ 848.0
O&R | Electric
Public Utilities, General Disclosures [Line Items]
Other revenue sources	0.8
Accrued unbilled revenue	11.3	18.6	$ 3.4	$ 6.9		$ 18.6
Deferral of net increase (decrease) to regulatory assets	$ 8.9	$ 10.2	15.4	9.4
Earnings sharing		9.70%				9.70%
Earnings sharing, threshold limit						$ 1.2
Common equity ratio						48.00%
Recovery of late payment charges, period (in years)						3 years
Recovery of late payment charges, amount						$ 2.2
Recovery of late payment charges, return on equity threshold rate						0.05%
O&R | Electric | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Earnings sharing					10.25%
Common equity ratio					48.00%
Difference in property taxes (percent)					90.00%
Regulatory assets usefull life					15 years
Uncollecetible expenses, threshold amount					$ 0.9
Surcharge recovery threshold percentage					50.00%
O&R | Electric | Year 1
Public Utilities, General Disclosures [Line Items]
Base rate changes						$ 4.9
Amortization to income of net regulatory assets						(11.8)
Potential earnings adjustment mechanism incentives						3.3
Average rate base						$ 1,021.0
Weighted average cost of capital (after-tax)						6.77%
Authorized return on common equity						9.20%
Actual return on common equity, percent						8.96%
Cost of long-term debt (percent)						4.58%
Requested rate increase (decrease), amount						$ 11.7
Regulatory assets, amortization period (in years)		5 years				5 years
O&R | Electric | Year 1 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations						$ 1,175.0
O&R | Electric | Year 1 | Maximum
Public Utilities, General Disclosures [Line Items]
Negative revenue adjustments						4.3
O&R | Electric | Year 1 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes					$ (13.1)
Amortization to income of net regulatory assets					(4.5)
Potential earnings adjustment mechanism incentives					3.9
Average rate base					$ 1,293.0
Weighted average cost of capital (after-tax)					7.25%
Authorized return on common equity					9.75%
Actual return on common equity, percent					8.98%
Cost of long-term debt (percent)					4.95%
Requested rate increase (decrease), amount					$ 0.0
Deferral, annual maximum (not more than) (percent)					1000.00%
O&R | Electric | Year 1 | Scenario, Forecast | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 1,398.0
O&R | Electric | Year 1 | Scenario, Forecast | Maximum
Public Utilities, General Disclosures [Line Items]
Negative revenue adjustments					7.6
O&R | Electric | Year 2
Public Utilities, General Disclosures [Line Items]
Base rate changes						16.2
Amortization to income of net regulatory assets						(13.5)
Potential earnings adjustment mechanism incentives						2.3
Average rate base						$ 1,044.0
Weighted average cost of capital (after-tax)						6.73%
Actual return on common equity, percent						8.73%
Cost of long-term debt (percent)						4.51%
Requested rate increase (decrease), amount						$ 11.7
O&R | Electric | Year 2 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations						1,198.0
O&R | Electric | Year 2 | Maximum
Public Utilities, General Disclosures [Line Items]
Negative revenue adjustments						4.4
O&R | Electric | Year 2 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes					24.8
Amortization to income of net regulatory assets					(5.4)
Potential earnings adjustment mechanism incentives					4.7
Average rate base					$ 1,393.0
Weighted average cost of capital (after-tax)					7.28%
Cost of long-term debt (percent)					5.01%
Requested rate increase (decrease), amount					$ 17.7
Deferral, annual maximum (not more than) (percent)					750.00%
O&R | Electric | Year 2 | Scenario, Forecast | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 1,471.0
O&R | Electric | Year 2 | Scenario, Forecast | Maximum
Public Utilities, General Disclosures [Line Items]
Negative revenue adjustments					8.5
O&R | Electric | Year 3
Public Utilities, General Disclosures [Line Items]
Base rate changes						23.1
Amortization to income of net regulatory assets						(15.2)
Potential earnings adjustment mechanism incentives						4.0
Other revenue sources		$ 2.6	$ 1.5	$ 2.7
Average rate base						$ 1,144.0
Weighted average cost of capital (after-tax)						6.72%
Actual return on common equity, percent						9.86%
Cost of long-term debt (percent)						4.49%
Requested rate increase (decrease), amount						$ 11.7
O&R | Electric | Year 3 | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations						1,304.0
O&R | Electric | Year 3 | Maximum
Public Utilities, General Disclosures [Line Items]
Negative revenue adjustments						$ 5.1
O&R | Electric | Year 3 | Scenario, Forecast
Public Utilities, General Disclosures [Line Items]
Base rate changes					44.1
Amortization to income of net regulatory assets					(6.4)
Potential earnings adjustment mechanism incentives					5.8
Average rate base					$ 1,646.0
Weighted average cost of capital (after-tax)					7.31%
Cost of long-term debt (percent)					5.08%
Requested rate increase (decrease), amount					$ 17.7
Deferral, annual maximum (not more than) (percent)					500.00%
O&R | Electric | Year 3 | Scenario, Forecast | Electric average excluding AMI
Public Utilities, General Disclosures [Line Items]
Net utility plant reconciliations					$ 1,737.0
O&R | Electric | Year 3 | Scenario, Forecast | Maximum
Public Utilities, General Disclosures [Line Items]
Negative revenue adjustments					$ 11.5